Abstract
Galaxy clusters in the present universe have a higher fraction of elliptical galaxies compared to low-density environments. To understand the origin of this environmental effect, observing an active phase of star formation in high-redshift clusters is thought to be effective. I will present an ALMA study obtained from spatially resolved CO J=2–1 line (0.4”-resolution) and 870 μm continuum (0.2”-resolution) observations of cluster galaxies in XMMXCS J2215.9-1738 at z = 1.46 (Ikeda et al. 2022). Our sample comprises 17 CO emitters within ∼0.5 Mpc (0.6R200) from the cluster center. The effective radii of both CO J=2–1 line and 870 μm dust continuum emissions are robustly measured for nine galaxies by modeling the visibilities. We find that the CO J=2–1 line emission in all of the nine galaxies is more extended than the dust continuum emission by a factor of 2.8 ± 1.4. The spatially resolved Kennicutt-Schmidt (KS) relation for our sample reveals that the central region (0 < r < Re,870μm) of galaxies tends to have a shorter gas depletion timescale, i.e. a higher star formation efficiency (SFE), compared to the extended region (Re,870μm < r < Re,CO). Overall, our result suggests that star formation activities are concentrated inside the extended gas reservoir, possibly resulting in the formation of a bulge structure. I will also present the recent result of gas kinematics using CO J=2-1 line, and CO J=5-4 line with 0.15"-resolution. We find the rotation curve steeply increases within 1 kpc, which is again suggestive of dense stellar component at the center.
